Nick, I stand corrected. The 97-99's had a 2.5, and the 2.7 was introduced in 2000 on the non-S. (I've been editing a book all day and the brain is deep fat french fried!)
Arona, thanks for the compliment! Sometimes I wonder if I run off more potential Boxster buyers than I do help out and this is nice to hear.
Heatfan, the 97-99 cars were typical "first year" production cars. They got a lot of bugs worked out in 98 and 99 with the top, certain engines manufactured during certain months (most have blown out and been replaced already), etc. The problem with Porsches in general is that they are not mass produced like a Camaro was made, so it takes longer to get things right.
Every year they improved this and that and make it a better car. The 987, released in 2005, was a giant leap of an overhaul. The models may not look very different, but they are in many, many ways. A far nicer interior is just the beginning of what is different.
This is why you will hear most every forum member who owns one tell you to buy the youngest model Boxster you can afford with the absolutely lowest mileage and most-detailed maintenance records you can find. You'll pay five grand more for that car, but it will give you years of trouble-free driving pleasure vs. "The damn thing is in the shop again! Can someone remind me why I bought an old, cheap Porsche one more time?"
By the way, this is the voice of experience talking here, and ask any of my buddies and they'll tell you I said these exact words for the first two years of ownership.
Like I wrote before, this is an amazing car and you should definitely buy one if you want the best mid-engine convertible on the planet. However, don't be penny-wise and pound-foolish. Spend it up front on a nicer car or spend it later on a not-so-nice car is the way it always works out with just about any automotive purchase.